The present invention relates to a power amplifier, and to a system, a device and a method for pulse width modulation.
Modulation is the change of signal parameters of a carrier as a function of a signal to be modulated (base band signal).
Demodulation is a further modulation process that serves to retrieve the base band signal.
In a typical configuration of a communications system, a modulated signal is generated by a modulator provided at a corresponding terminal by using modulation from a carrier and a signal to be modulated. This modulated signal is, via a communication channel, transmitted to a demodulator provided at a further terminal.
As a carrier for the modulation, e.g., appropriate sinusoidal waves may be used, or—to an increasing degree—appropriate pulses.
In the case of sinusoidal carriers, the following signal parameters may, for instance, be influenced for modulation: amplitude, frequency, zero phase, etc., and in the case of pulse carriers, for instance, the signal parameters pulse amplitude, pulse frequency, pulse phase, and/or pulse duration (pulse width).
Pulse duration or pulse width modulation methods (PDM or PWM methods) are, for instance, used in entertainment electronics, e.g., for the modulation of audio and video signals.
A known method for digital pulse width modulation is for instance described in Jorge Varona, ECE University of Toronto: “Power Digital to Analog Conversion Using Sigma Delta and Pulse Width Modulations”.
Further, DE 10350336.6, U.S. Ser. No. 10/976,074, Infineon Technologies, inventor: Ch. Braun, describes a pulse width modulation method in which a pulse width modulated signal is used as a feedback signal in a digital loop.
With a corresponding pulse width modulated signal for instance a Class-D amplifier may be triggered.
Conventional Class-D power amplifiers in general have an input stage and an output stage. In Class-D power amplifiers, the output stages are conventionally operated in a switching mode. This means that the output stage is either switched on or switched off.
In conventional Class-D power amplifiers, an (analogue digital) input signal is converted into a periodic sequence of pulses having a predetermined pulse frequency. The pulse width of a respective pulse e.g., may represent the amplitude of the input signal at one point in time. The pulse frequency is chosen to be at least twice as large as the maximum frequency of the input signal. Typically, the pulse frequency is e.g., ten or more times higher than the highest frequency of the input signal.
The above periodic sequence of pulses—i.e., the pulse width modulated signal—is input to a high power switching device, which generates a high power replica of the pulse width modulated signal. This amplified pulse width modulated signal is e.g., fed to a filter, which e.g., removes the high-frequency switching components of the PWM signal.
Conventionally, differential pulse width modulation is used in Class-D power amplifiers.
Class-D power amplifiers e.g., may be used for stereo audio signal amplification.
In the case of differential pulse width modulation, a Class-D stereo power amplifier in general has four outputs, which may be connected via a respective pair of cables to a respective pair of loudspeakers.
However, in the case of stereo earphones or headphones, Class-D power amplifiers with just three outputs are needed (as earphones or headphones in general only have three inputs, which are to be connected via three respective cables or wires to the respective Class-D power amplifier outputs).
Hence, if a Class-D power amplifier is to be provided which is to be used for earphones or headphones, conventionally, a respective DC middle potential is generated, which is provided at a first one of the above three Class-D power amplifier outputs. At a second one of the above three Class-D power amplifier outputs, e.g., a signal representing the “left” stereo channel is provided, and at a third one of the above three Class-D power amplifier outputs, e.g., a signal representing the “right” stereo channel. However, the disturbance behaviour and/or the loss factor of such Class-D power amplifiers may be relatively bad.
For these or other reasons, there is a need for the present invention.